If you would like to transform the following phrase into a math expression, you can do it like this:
8 less than a number is no more than 14 and no less than 5
a number ... n
8 less ... - 8
no more than 14 .... < 14
no less than 5 ... > 5
Now you just have to put this together: 5 < n - 8 < 14
If 5 and 14 are included: 5 <= n - 8 <= 14